Laying concrete on soil involves careful preparation and a step-by-step process to ensure a durable and stable surface. The key is properly preparing the ground before the concrete is poured.
Here are the essential steps for laying concrete on soil:
Preparing the Site for Concrete
Proper site preparation is the foundation for a successful concrete slab. It ensures the ground is stable, level, and ready to support the concrete.
Step 1: Clearing the Site
Begin by clearing the area where the concrete will be laid. This involves removing all vegetation, grass, rocks, debris, and any existing structures. The ground needs to be bare soil.
Step 2: Marking Out and Excavating
Next, mark out the exact dimensions of the area for the concrete slab using stakes and string. This defines the perimeter. Once marked, excavate the area to the required depth. The excavation depth depends on the planned concrete thickness and the type of base material you will use. Typically, this is deep enough for the concrete slab plus the base layer.
Step 3: Compacting the Soil
After excavation, the underlying soil must be compacted. This is a crucial step to prevent settling, which can lead to cracked concrete later. Use a plate compactor or a hand tamper to achieve a firm, stable sub-base. Compact the soil thoroughly across the entire excavated area.
Building the Base and Framework
Once the soil is compacted, you build up the foundation layer and create the mold for the concrete.
Step 4: Laying the Base
Lay a base layer of granular material, such as crushed gravel or aggregate, over the compacted soil. This layer provides drainage and further stability. Spread the material evenly to the required thickness (often 4-6 inches) and then compact it thoroughly using the compactor again.
Step 5: Building the Framework
Construct a framework, often called formwork, around the perimeter of the excavated and based area. This framework, usually made from wooden boards or metal forms, acts as a mold to hold the wet concrete in place and define the shape and thickness of the slab. Ensure the forms are securely staked and level.
Pouring and Finishing the Concrete
With the preparation complete, you are ready to pour the concrete.
Step 6: Pouring the Concrete
Mix and pour the concrete into the prepared framework. Use a shovel or rake to spread the concrete evenly, ensuring it fills the forms completely, especially in the corners. Use a straight board (screed) to level the concrete surface by moving it back and forth across the top of the forms.
Step 7: Finishing Touches
After screeding, perform the finishing touches. This typically involves:
- Floating: Using a float tool to smooth the surface and bring 'cream' (fine cement paste) to the top.
- Edging: Using an edge tool to create smooth, rounded edges.
- Jointing: Cutting control joints into the concrete surface at appropriate intervals. These joints help control where the concrete cracks as it shrinks during curing, directing the cracks along the joint lines instead of randomly across the slab.
- Troweling: Using a trowel for a final smooth finish, if desired.
Once finished, the concrete needs to cure properly. Keep it moist for several days by covering it with plastic, wet burlap, or using curing compounds to prevent it from drying out too quickly, which can weaken the concrete.
Laying concrete on soil requires attention to detail at every step, particularly in site preparation and base construction, to create a long-lasting concrete slab.
